The present invention relates to a method for functional diagnosis of a separator for separating oil present in a blow-by gas flow from a crankcase in a combustion engine. The combustion engine is preferably used in a vehicle.
In the field of vehicle exhaust gas cleaning, the industry faces the delicate balance of providing an adequate effect from the engine, which is demanded by some consumers, while not emitting high quantities of harmful emissions, such as NOx, COx, hydrocarbons, particulates and the like, which is demanded by consumers and the manufacturer's own environmental policies. The demand to have a combustion engine and an exhaust gas cleaning system which strives towards zero emission is however not only driven by the consumers but also by the legislators. Hence an increased awareness of the need for environmental-friendly solutions in the vehicle industry is crystallized in a more restrictive legislation with respect to permitted emissions. An example of such legislation is the need for on-board diagnostics (OBD), although not implemented around the world yet. These restrictions provide new challenges and opportunities to the vehicle industry.
In short, some legislation in some countries demands that the on-board diagnosis system should detect any part of the system which is not functioning properly, is disconnected or not connected properly after e.g. service. This imparts a need for providing a number of sensors to different parts of the combustion engine, the vehicle and the on-board computer system. This results in a steadily increasing number of sensors and a more complex analysis methodology which requires more and more processing power from the on board computer system.
In patent EP 1,085,945 B1 a method for cleaning gases is disclosed. The patent discloses a separator with a plurality of rotating discs driven by pressurized air, pressurized lubricating oil, pressurized cooling water or pressurized fuel. The patent is however silent about how to perform any kind of quality control of the separator. The patent publication US 2001/0047801 discloses a method for performing a functional diagnosis, i.e. a functionality evaluation test, on a ventilation system of a crankcase of an internal combustion engine. The system comprises a pulse valve which is controlled as a function of the pressure in the crankcase, the pressure is determined using a pressure sensor. When a high pressure is detected, the pulse valve is opened to permit the exhaust gas to be discharged via an intake pipe. Based on the pressure characteristics it can be detected for example whether the oil level is sufficient, if there is a leak in the ventilation system or whether the internal combustion engine exhibits increased wear. The document is however silent about how to perform any functional diagnosis on a separator for separating oil from a gas. Hence it would seem that there is a need for a method for performing a functional diagnosis on a separator to meet the increasing demands from consumers, legislators as well as the manufacturers own environmental policy.
The above mentioned drawbacks are at least partly solved by means of a method for functional diagnosis of a separator, the separator being arranged to separate oil present in a blow-by gas from a crankcase in a combustion engine. The crankcase comprises a crankcase pressure sensor, and is in fluid communication with the separator. The method comprises the steps; detecting a first output signal of the crankcase pressure sensor at a first operational point or interval; comparing the first output signal of the crankcase pressure sensor with at least one reference value or signal; wherein the comparison between the first output signal of the crankcase pressure sensor and the at least one reference value or signal provides the functional diagnosis of the separator. The method according to the present invention provides for a functional diagnosis of a separator without the addition of extra sensors, instead existing sensors are better utilized. By using existing sensors already arranged in the combustion engine, in this case the crankcase pressure sensor, fewer manufacturing steps are needed when manufacturing the engine, cost is reduced and emissions dangerous to the environment are more efficiently controlled.
The at least one reference value or signal can be representative of a crankcase pressure derived at a second operational point or interval or optionally be a second output signal of the crankcase pressure sensor at a second operational point or interval. This latter embodiment of the present invention provides for a dynamic comparison between the first registered signal and the reference signal, as both of them are registered during the run of the combustion engine. During detection of the first output signal of the crankcase pressure sensor, the combustion engine is preferably run at a substantially constant engine speed or engine torque, preferably at idle. Optionally the at least one reference value or signal is derived from the output signal of the crankcase pressure sensor when the combustion engine runs in a working mode. By the term working mode is hereby meant when the engine is subjected to torque, i.e. when driving forward or backward.
A first average value over an operational interval can be determined from the output signal of the crankcase pressure sensor; the first average value is then compared with the at least one reference value or signal. This provides for a more secure and predictable comparison since a more reliable value is obtained from the measurement. Likewise an average of the at least one reference value can be determined over an operational interval; the first average value is then compared the average reference value. The average reference value is in an embodiment of the present invention equivalent with substantially the lowest value of the output signal of the crankcase pressure sensor. The operational interval can be within the time interval of 5-240 seconds, preferably 5-60 seconds, to provide an accurate measurement.
In an embodiment of the present invention, a response action is initiated as a consequence of the outcome of the functional diagnosis. Preferably, if the difference between the output signal and the at least one reference value or signal does not exceed a predetermined threshold value, a response action is initiated.
In one embodiment of the present invention the first output signal of the crankcase pressure sensor is accepted as a first output signal, with respect to the functional diagnosis, if the received numbers of measured data points exhibit an individual deviation of about maximum 10%, with respect to each other. As an alternative, the first output signal can be accepted as a first output signal, with respect to the functional diagnosis, when a substantially constant pressure (or delta pressure) is detected over a specified period of time. This acceptance step ensures that the registered pressure signal is collected at a point or in an interval in which the separator clearly has a proper function. For the purpose of the above, a first operational point or interval may comprise a continuously received number of measured data points.
The above mentioned reference points have been measured dynamically, i.e. during the run of the combustion engine, however, the at least one reference value can be a predetermined reference value. As such the predetermined reference value can be selected to represent different separators with different degree of malfunction. For instance the predetermined reference value can be representative of a separator having a grade of efficiency of less than 50% of a separator during otherwise normal operations. With the term “during otherwise normal operations” means in this context a separator with a reduced efficiency, i.e. with a malfunction, compared with an identical separator without the malfunction but exposed to the same operational conditions.
In an embodiment of the present invention, the first output signal from the crankcase pressure sensor, and preferably the first average value, is compared with a first and a second reference value, interval or signal. The first reference value is a dynamic reference value and the second reference value is a predetermined reference value. Optionally both the first and the second reference value be dynamic or both may be predetermined.
To provide for accurate readings and better functional diagnosis, the output signal of the crankcase pressure sensor can be compared to an ambient pressure, the ambient pressure being the ambient air pressure around the combustion engine. This adaptation of the crankcase pressure removes the influence of the ambient air which can disturb the readings of the crankcase pressure, e.g. when driving on roads at high altitude above sea level.
As mentioned above the separator can have many different configurations. For the purpose of the present invention it is however preferred that the separator comprises an oil separation member, such as a rotating disc, rotatably arranged in the separator. The oil separation member can be rotated by rotating means such as a turbine drive connector driven by main galley engine oil, cooling liquid, pressurized air, lubricating crankcase oil or the like, or optionally driven directly by an electrical motor or by a fan belt or the like.
The reference value or signal can be a second output signal of said crankcase pressure sensor at a second operational point or interval. While a change in the energy input of the rotary means and thereby the efficiency of the separator has been made between the first and said second output signal. This change in energy input, e.g. by changing the pressure of a pressurized fluid when the rotating member is driven by a pressurized fluid, the functional diagnosis of the separator can be further improved as a determined increase in energy input should cause a corresponding increase in pressure.
The present invention also relates to the use of a crankcase pressure sensor for functional diagnosis of a separator, the separator is a separator for separating oil present in a blow-by gas from a crankcase in a combustion engine.
The present invention also relates to a method for functional diagnosis of a separator for separating oil present in a blow-by gas flow from a crankcase in a combustion engine. The crankcase comprises a crankcase pressure sensor, and is in fluid communication with the separator, the separator comprises a blow-by gas inlet- and outlet openings. The method comprises the steps of; detecting an ambient temperature, the ambient temperature being the temperature around the combustion engine; detecting the blow-by gas temperature at the outlet opening of the separator or downstream of the outlet opening; comparing the ambient temperature with the blow-by gas temperature, wherein the detected relation between the ambient temperature and the blow-by gas temperature provides the functional diagnosis of the separator. Preferably is the blow-by gas temperature detected at the outlet opening of the separator. The ambient temperature and the blow-by gas temperature is preferably detected at a first operational point and thereafter compared to an ambient temperature and a blow-by gas temperature detected at a second operational point. The ambient temperature(s) and the blow-by gas temperature(s) can further be compared with the engine speed. The engine speed is detected at the same operational point(s) in time as the ambient temperature(s) and the blow-by gas temperature(s).
By the term “operational point” is meant a point when the system is running, preferably at a point in time.